homework/bitmap.c

   1 #include <limits.h>    /* for CHAR_BIT */
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>    /* for memset() */
   5
   6 int is_blk_free(const unsigned char *array, unsigned int nblk);
   7 void print_blks(const unsigned char *array, unsigned int nblks);
   8 void diep(const char *s);
   9
  10 int main(int argc, char *argv[])
  11 {
  12     unsigned char *array;
  13     unsigned int i, narr, nblks, u;
  14
  15     /* Check argument count */
  16     if (argc != 2) {
  17         fprintf(stderr, "Usage: %s nblocks\n", argv[0]);
  18         exit(EXIT_FAILURE);
  19     }
  20
  21     /* Get number of blocks */
  22     nblks = (unsigned int) strtoul(argv[1], NULL, 10);
  23     u = nblks - CHAR_BIT * (nblks / CHAR_BIT);
  24     if (u == 0)
  25         narr = nblks / CHAR_BIT;
  26     else
  27         narr = nblks / CHAR_BIT + 1;
  28     printf("nblks = %u\tnarr = %u\n", nblks, narr);
  29
  30     /* Allocate memory for char bitmap */
  31     array = malloc(narr);
  32     if (array == NULL)
  33         diep("malloc");
  34
  35     /* Initialize all bits to 0 representing free blocks */
  36     memset(array, 0, narr);
  37
  38     /* Print blocks' status */
  39     print_blks(array, nblks);
  40
  41     /* Flag all blocks as used */
  42     for (i = 0; i < narr; i++)
  43         array[i] = 0xFF;
  44     print_blks(array, nblks);
  45
  46     /* Free bitmap */
  47     free(array);
  48
  49     return EXIT_SUCCESS;
  50 }
  51
  52 int is_blk_free(const unsigned char *array, unsigned int nblk)
  53 {
  54     unsigned int idx, u;
  55
  56     idx = nblk / CHAR_BIT;
  57     u = nblk - CHAR_BIT * idx;
  58     printf("blk %u is in array %u and bitpos %u\n",
  59            nblk, idx, u);
  60
  61     return ((array[idx] & (1 << u)) == 0);
  62 }
  63
  64 void print_blks(const unsigned char *array, unsigned int nblks)
  65 {
  66     unsigned int i;
  67
  68     for (i = 0; i < nblks; i++)
  69         printf("blk[%04u] = %s\n",
  70                i, is_blk_free(array, i) ? "FREE" : "USED");
  71 }
  72
  73 void diep(const char *s)
  74 {
  75     perror(s);
  76     exit(EXIT_FAILURE);
  77 }